Plasma treatment method and apparatus

ABSTRACT

A plasma treatment method comprising exhausting a process chamber so as to decompress the process chamber, mounting a wafer on a suscepter, supplying a process gas to the wafer through a shower electrode, applying high frequency power, which has a first frequency f 1  lower than an inherent lower ion transit frequencies of the process gas, to the suscepter, and applying high frequency power, which has a second frequency f 2  higher than an inherent upper ion transit frequencies of the process gas, whereby a plasma is generated in the process chamber and activated species influence the wafer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a plasma treatment method by whichsubstrates such as semiconductor wafers are etched or sputtered underplasma atmosphere. It also relates to a plasma treatment apparatus forthe same.

2. Description of the Related Art

Recently, semiconductor devices are more and more highly integrated andthe plasma treatment is therefore asked to have a finer workability intheir making course. In order to achieve such a finer workability, theprocess chamber must be decompressed to a greater extent, plasma densitymust be kept higher and the treatment must have a higher selectivity. Inthe case of the conventional plasma treatment methods, however, highfrequency voltage becomes higher as output is made larger, and ionenergy, therefore, becomes stronger than needed. The semiconductor waferbecomes susceptible to damage, accordingly. Further, the process chamberis kept about 250 mTorr in the case of the conventional methods and whenthe degree of vacuum in the process chamber is made higher (or theinternal pressure in the chamber is made smaller), plasma cannot be keptstable and its density cannot be made high.

SUMMARY OF THE INVENTION

When gases are made plasma, the action of ions in the plasma becomesdifferent, depending upon frequencies of high frequency power. In short,ion energy and plasma density can be controlled independently of theother when high frequency power having two different frequencies isapplied to process gases. However, ions (loaded particles) easily runfrom plasma to the wafer at a frequency band, but it becomes difficultfor them to run from the plasma sheath to the wafer at another frequencyband (or transit frequency zone). The so-called follow-up of ionsbecomes unstable.

Particularly molecular gases change their dissociation, depending uponvarious conditions (such as kinds of gas, flow rate, high frequencypower applying conditions and internal pressure and temperature in theprocess chamber), and the follow-up of ions in the plasma sheath changesin response to this changing dissociation. Further, the follow-up ofions at the transit frequency zone also depends upon their volume (ormass). Particularly in the case of molecular gases used in etching andCVD, the dissociation of gas molecules progresses to an extent greaterthan needed when electron temperature becomes high with a littleincrease of high frequency power, and the behavior of ions in the plasmasheath changes accordingly. Plasma properties such as ion currentdensity become thus unstable and the plasma treatment becomes uneven,thereby causing the productivity to be lowered.

When the frequency of high frequency power is only made high to increaseplasma density, the dissociation of gas molecules progresses to theextent greater than needed. It is therefore desirable that the plasmadensity is raised not to depend upon whether the frequency is high orlow.

An object of the present invention is therefore to provide plasmatreatment method and apparatus capable of controlling both of thedissociation of gas molecules and the follow-up of ions and also capableof promoting the incidence of ions onto a substrate to be treated.

Another object of the present invention is to provide plasma treatmentmethod and apparatus capable of raising the plasma density with smallerhigh frequency power not to damage the substrate to be treated.

According to the present invention, there can be provided a plasmatreatment method of plasma-treating a substrate to be treated underdecompressed atmosphere comprising exhausting a process chamber;mounting the substrate on a lower electrode; supplying plasma generatinggas to the substrate on the lower electrode through an upper electrode;applying high frequency power having a first frequency f₁, lower thanthe lower limit of ion transit frequencies characteristic of processgas, to the lower electrode; and applying high frequency power having asecond frequency, higher than the upper limit of ion transit frequenciescharacteristic of process gas, to the upper electrode, whereby a plasmagenerates in the process chamber and activated species influence thesubstrate to be treated.

It is preferable that the first frequency f₁ is set lower than 5 MHz,more preferably in a range of 100 kHz-1 MHz. It is also preferable thatthe second frequency f₂ is set higher than 10 MHz, more preferably in arange of 10 MHz-100 MHz.

High frequency power having the frequency lower than the lower limit ofion transit frequencies is applied to the lower electrode. Therefore,the follow-up of ions becomes more excellent and ions can be moreefficiently accelerated with a smaller power. In addition, both of ionand electron currents change more smoothly. Further, the follow-up ofions does not depend upon kinds of ion. The plasma treatment can be thusmade more stable even when the degree in the process chamber and therate of gases mixed change. On the other hand, high frequency powerhaving the frequency higher than the upper limit of ion transitfrequencies is applied to the upper electrode. Therefore, ions can beleft free from frequencies of their transit frequency zone to therebyenable more stable plasma to be generated.

Ion transit frequency zones of process gases used by the plasmatreatment in the process, such as etching, CVD and sputtering, of makingsemiconductor devices are almost all in the range of 1 MHz-10 MHz.

Impedances including such capacitive components that the impedancerelative to high frequency power becomes smaller than several kΩ andthat the impedance relative to relatively low frequency power becomeslarger than several Ω are arranged in series between the upper electrodeand its matching circuit and between them and the ground. Current isthus made easier to flow to raise the plasma density and ion control.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention and, together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 is a block diagram showing the plasma etching apparatus accordingto an embodiment of the present invention;

FIG. 2 is a flow chart showing the plasma etching method according to anembodiment of the present invention;

FIG. 3 shows a waveform of frequency applied to an upper (or second)electrode;

FIG. 4 shows a waveform of frequency applied to a lower (or first)electrode (or suscepter);

FIG. 5 is a graph showing transit frequency zones of various gases;

FIG. 6 is a block diagram showing the plasma etching apparatus accordingto another embodiment of the present invention;

FIG. 7 is a block diagram showing the plasma etching apparatus accordingto a further embodiment of the present invention;

FIG. 8 is a block diagram showing the plasma etching apparatus accordingto a still further embodiment of the present invention;

FIG. 9 is a vertically-sectioned view showing a housing and a ringmember of the plasma etching apparatus;

FIG. 10 is a vertically-sectioned view showing the ring member beingcleaned;

FIG. 11 is a vertically-sectioned view showing the ring member beingcleaned;

FIG. 12 is a perspective view showing an upper shower electrode and asemiconductor wafer dismantled;

FIG. 13 is a block diagram showing the plasma etching apparatusaccording to a still further embodiment of the present invention;

FIG. 14 is a vertically-sectioned view showing the plasma etchingapparatus when the suscepter is lowered;

FIG. 15 is a vertically-sectioned view showing the plasma etchingapparatus when the suscepter is lifted;

FIG. 16 is a partly-sectioned view showing a wafer carry-in and -outgate and a baffle member;

FIG. 17 is a partly-sectioned view showing the wafer carry-in and -outgate and another baffle member;

FIG. 18 is a block diagram showing the plasma etching apparatusaccording to a still further embodiment of the present invention;

FIG. 19 is a perspective view showing a cover for the upper showerelectrode;

FIG. 20 is a perspective view showing another cover for the upper showerelectrode;

FIG. 21 is a vertically-sectioned view showing the cover for the uppershower electrode;

FIG. 22 is a plan view showing the cover for the upper shower electrode;

FIG. 23 shows how the cover is attached to the upper shower electrode;

FIG. 24 shows how the cover is detached from the upper shower electrode;

FIG. 25 is a sectional view showing the cover being cleaned;

FIG. 26 is a sectional view showing a further cover;

FIG. 27 is a sectional view showing a still further cover;

FIG. 28 is a sectional view showing a still further cover;

FIG. 29 is a block diagram showing a magnetron plasma etching apparatusin which plasma is being generated;

FIG. 30 is a perspective view showing a baffle member arranged on theside of the suscepter;

FIG. 31 is a vertically-sectioned view showing a hole formed in thebaffle member;

FIG. 32 is a vertically-sectioned view showing another hole formed inthe another baffle member;

FIG. 33 shows plasma generated in the conventional apparatus;

FIG. 34 is intended to explain the relation of the process chamber tomagnetic field generated by a permanent magnet;

FIG. 35 is a block diagram showing the plasma etching apparatusaccording to a still further embodiment of the present invention;

FIG. 36 is a block diagram showing the inside of a vaporizer;

FIG. 37 is a sectional view showing another vaporizer;

FIG. 38 is a sectional view showing a further vaporizer;

FIG. 39 is a perspective view showing a still further vaporizer;

FIG. 40 is a sectional view showing a pipe in which plural kinds of gasare mixed;

FIG. 41 is a block diagram showing a plasma CVD apparatus provided withthe vaporizer;

FIG. 42 is a sectional view showing the inside of the conventionalvaporizer; and

FIG. 43 is a graph showing the change of gas flow rate at the initialstage of gas supply.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Some embodiments of the present invention will be described withreference to the accompanying drawings. Referring to FIGS. 1 through 5,a first embodiment will be described.

A process chamber 2 of an etching treatment apparatus 1 is assembled byalumite-processed aluminium plates. It is earthed and a suscepter 5insulated by an insulating plate 3 is arranged in it. The suscepter 5 issupported by its bottom through the insulating plate 3 and a support 4.

A coolant chamber 6 is formed in the suscepter support 4. It iscommunicated with a coolant supply supply (not shown) through inlet andoutlet pipes 7 and 8 and coolant such as liquid nitrogen is circulatedbetween it and the coolant supply supply.

An internal passage 9 is formed in a suscepter assembly which comprisesthe insulating plate 3, the support 4, the suscepter 5 and anelectrostatic chuck 11, and heat exchanger gas such as helium gas issupplied from a gas supply supply (not shown) to the underside of awafer W through it.

The top center portion of the suscepter 5 is swelled and theelectrostatic chuck 11, same in shape as the wafer W, is mounted on theswelled portion of the suscepter 5. A conductive layer 12 of theelectrostatic chuck 11 is sandwiched between two sheets of highmolecular polyimide film. It in connected to a 1.5 kV DC high voltagepower supply 13 arranged outside the process chamber 2.

A focus ring 14 is arranged on the top of the suscepter 5 along theouter rim thereof, enclosing the wafer W. It is made of insulatingmaterial not to draw reactive ions.

An upper electrode 21 is opposed to the top of the suscepter assembly.Its electrode plate 24 is made of SiC or amorphous carbon and itssupport member 25 is made by an alumite-process aluminium plate. Itsunderside is separated from the wafer W on the suscepter assembly byabout 15-20 mm. It is supported by the top of the process chamber 2through an insulating member 22. A plurality of apertures 23 are formedin its underside.

A gas inlet 26 is formed in the center of the support 25 and a gas inletpipe 27 is connected to it. A gas supply pipe 28 is connected to the gasinlet pipe 27. The gas supply pipe 28 is divided into three which arecommunicated with process gas supply sources 35, 36 and 37,respectively. The first one is communicated with the CF₄ gas supplysource 35 through a valve 29 and a mass flow controller 32. The secondone with the O₂ gas supply supply 36 through a valve 30 and a mass flowcontroller 33. The third one with the N₂ gas supply supply 37 throughvalve 31 and a mass flow controller 34.

An exhaust pipe 41 is connected to the bottom of the process chamber 2.An exhaust pipe 44 is also connected to the bottom of an adjacent loadlock chamber 43. Both of them are communicated with a common exhaustmechanism 45 which is provided with a turbo molecular pump and the like.The load lock chamber 43 is connected to the process chamber 2 through agate valve 42. A carrier arm mechanism 46 is arranged in the load lockchamber 43 to carry the wafers W one by one between the process chamber2 and the load lock chamber 43.

A high frequency power applier means for generating plasma in theprocess chamber 2 will be described.

A first oscillator 51 serves to oscillate high frequency signal having afrequency of 800 kHz. A circuit extending from the oscillator 51 to thelower electrode (or suscepter) 5 includes a phase controller 52, anamplifier 53, a matching unit 54, a switch SW₁ and a feeder rod 55. Theamplifier 53 is an RF generator and the matching unit 54 includes adecoupling capacitor. The switch SW₁ is connected to the feeder rod 55.A capacitance 56 is arranged on an earthed circuit of the feeder rod 55.The phase controller 52 houses a bypass circuit (not shown) and achangeover switch (not shown) therein to enable signal to be sent fromthe first oscillator 51 to the amplifier 53 through the bypass circuit.High frequency signal oscillated is applied to the suscepter 5 throughthe phase controller 52, the amplifier 53, the matching unit 54 andfeeder rod 55.

On the other hand, a second oscillator 61 serves to oscillate highfrequency signal having a frequency of 27 MHz. A circuit extending fromthe oscillator 61 to the upper (or shower) electrode 21 includes anamplitude modulator 62, an amplifier 63, a matching unit 64, a switchSW₂ and a feeder rod 65. The amplitude modulator 62 is connected to asignal circuit of the second oscillator 61 and also to that of the firstoscillator 51. It houses a bypass circuit (not shown) and a changeoverswitch (not shown) in it to enable signal to be sent from it to theamplifier 63 through the bypass circuit. The amplifier 63 is an RFgenerator and the matching unit 64 includes a decoupling capacitor. Theswitch SW₂ is connected to the feeder rod 65. A capacitance 66 and aninductance 67 are arranged on an earthed circuit of the feeder rod 65.High frequency signal oscillated is applied to the upper electrode 21through the amplitude modulator 62, the amplifier 63, the matching unit64 and the feeder rod 65. High frequency signal having the frequency of800 kHZ can also be applied, as modulated wave, to the amplitudemodulator 62.

The reason why the earthed circuit of the feeder rod 55 includes noinductance resides in that the electrostatic chuck 11, the gas passage9, the coolant chamber 6, lifter pins (not shown) and the like areincluded in the lower electrode signal transmission circuit, that thefeeder rod 55 itself is long, and that the suscepter 5 itself has largeinductance accordingly.

The amplifiers 51 and 64 are arranged independently of the other.Therefore, voltages applied to the upper electrode 21 and the suscepter5 can be changed independently of the other.

Referring to FIG. 2, it will be described how silicon oxide film (SiO₂)on the silicon wafer W is plasma-etched.

Both of the load lock chamber 43 and the process chamber 2 are exhaustedto substantially same internal pressure. The gate valve 42 is opened andthe wafer W is carried from the load lock chamber 43 into the processchamber 2 (step S1). The gate valve 42 is closed and the process chamber2 is further exhausted to set its internal pressure in a range of 10-250mTorr (step S2).

The valves 29 and 30 are opened, and CF₄ and O₂ gases are introducedinto the process chamber 2. Their flow rates are controlled and they aremixed at a predetermined rate. The (CF₄ +O₂) mixed gases are supplied tothe wafer W through apertures 23 of the upper shower electrode 21 (stepS3). When the internal pressure in the chamber 2 becomes stable at about1 Pa, high frequency voltages are applied to the upper and lowerelectrodes 21 and 5 to generate plasma between them.

Frequencies of high frequency power applied to the upper and lowerelectrodes 21 and 5 to generate plasma are controlled as follows (stepS4).

The switches SW₁ and SW₂ are opened to disconnect (OFF) the capacitance56 from the feeder rod 55 and the capacitance 66 and the inductance 67from the feeder rod 65. When the oscillators 61, 51, the amplitudemodulator 62 and the amplifiers 63, 53 are made operative under thisstate, high frequency power having a certain waveform is applied to theupper electrode 21. High frequency power having a frequency same as orhigher than the higher one of upper ion transit frequenciescharacteristic of CF₄ and O₂ gases is applied to the upper electrode 21.High frequency power having a waveform shown in FIG. 3, for example, isapplied to the upper electrode 21. Plasma is thus generated.

On the other hand, high frequency power having a certain waveform isapplied to the lower electrode 5 by the oscillator 51. High frequencypower having a frequency same as or lower than the lower one of iontransit frequencies characteristic of CF₄ and O₂ gases is applied to thelower electrode 5. High frequency power having a waveform shown in FIG.4, for example, is applied to the lower electrode. Ions in plasma arethus accelerated and drawn to the wafer W, passing through the plasmasheath, to thereby act on the wafer W.

The high frequency by which plasma is generated has the waveform shownin FIG. 3 in this case. Therefore, the dissociation of gases introducedinto the process chamber 2 is not advanced to an extent greater thanneeded. In addition, the frequency of 800 kHz by which ions in plasmaare accelerated and drawn to the wafer W can be controlled in phase bythe phase controller 52. Ions can be thus drawn to the wafer W beforethe dissociation of gases progresses to the extent greater than needed.When ions most suitable for etching are generated, therefore, they canbe made incident onto the wafer W. When they are caused to act on thewafer W while cooling it, therefore, anisotropic etching having a highaspect rate can be realized.

The phase control of the high frequency power (frequency: 800 kHz)applied to the lower electrode may be based on a state under which thedissociation of gases does not progress to the extent greater thanneeded or a state under which the dissociation of gases progresses tothe final stage, they are then combined again and become radicalssuitable for etching.

Further, it may be arranged that a dummy wafer DW is used and that thetreatment is carried out while confirming the extent to which the phaseof the high frequency 800 kHz is shifted. The timing at which the phaseof the high frequency 800 kHz is shifted may be previously set in thiscase, depending upon kinds of process gases, etching, coating and thelike.

When the end point of anisotropic etching is detected (step S5),exhaust, process gas introducing and plasma control steps S6, S7 and S8are successively carried out to isotropically etch film on the wafer W.The exhaust step S6 is substantially same as the above-described one S2.At the process gas introducing step S7, C₄ F₈, CHF₃, Ar and CO gases,for example, different from those at the above-described step S3, aresupplied to the process chamber 2.

At the plasma control step S8, plasma is controlled substantially asseen at the above-described step S4. When the end point of isotropicetching is detected (step S9), the applying of the high frequency poweris stopped and the process chamber 2 is exhausted while supplyingnitrogen gas into it (step S10). The gate valve 42 is opened and thewafer W is carried from the process chamber 2 into the load lock chamber43 (step S11).

Referring to FIG. 5, the plasma control steps S4 and S8 will bedescribed in more detail.

FIG. 5 is a graph showing ion transit frequency zones characteristic ofthree kinds of gases A, B and C, in which frequencies are plotted on thevertical axis. An ion transit frequency zone Az of gas A extends from anupper end Au to a lower end Al, an ion transit frequency zone Bz of gasB from an upper end Bu to a lower end Bl, and an ion transit frequencyzone Cz of gas C from an upper end Cu to a lower end C1. CHF₃ or CO gasis cited as gas A. Ar gas is cited as gas B. CF₄, C₄ F₈ or O₂ gas iscited as gas C. At least one or more gases selected from the groupconsisting of CF₄, C₄ F₈, CHF₃, Ar, O₂ and CO gases are used as processgas. In short, process gas may be one of them or one of mixed gases (CH₃+Ar+O₂), (CHF₃ +CO+O₂), (C₄ F₈ +Ar+O₂), (C₄ F₈ +CO+Ar+O₂) and (CF₄+CHF₃).

When mixed gases of A, B and C are used as process gas, the highfrequency power applied to the upper electrode has a frequency higherthan the highest one Bu of upper ion transit frequencies Au, Bu and Cuand the high frequency power applied to the lower electrode has afrequency lower than the lowest one Cl of lower ion transit frequenciesAl, Bl and Cl.

Another etching treatment method conducted using the above-describedetching treatment apparatus 1 will be described.

The switches SW₁ and SW₂ are closed or turned on to connect the signaltransmission circuits to their earthed circuits. High frequency signal(frequency: 800 kHz) is amplified directly by the amplifier 53,bypassing the phase controller 52, and applied to the suscepter 5through the matching unit 54. On the other hand, high frequency signal(frequency: 27 MHz) is amplified directly by the amplifier 63, bypassingthe amplitude modulator 62, and applied to the upper electrode 21 viathe matching unit 64 and the feeder rod 65.

Conventionally, the matching unit arranged on the side of the suscepteris matched relative to the high frequency of 800 kHz but it becomes highin impedance relative to the high frequency of 27 MHz applied from theupper electrode, thereby making it difficult for the high frequencyapplied from the upper electrode to flow to the suscepter. Plasma isthus scattered, so that the plasma density decreases.

In the apparatus 1, however, the capacitance 56 is arranged between thefeeder rod and the ground. A DC resonance circuit can be thus formedrelative to the high frequency applied from the upper electrode. Whenthe value of the capacitance 56 is adjusted, considering the constant ofa distributed constant circuit, therefore, composite impedance can bemade smaller than several Ω to thereby make it easy for the highfrequency applied from the upper electrode to flow to the suscepter 5.Therefore, current density can be raised and plasma density thusattained can also be raised.

On the other hand, the capacitance 66 and the inductance 67 are attachedto the feeder rod 65 arranged on the side of the upper electrode 21.Therefore, a DC resonance circuit is also provided relative to the highfrequency of 800 kHz, thereby making it easy for the high frequency 800kHz applied to the side of the suscepter 5 to flow to the upperelectrode 21. The incidence of ions in plasma onto the wafer W ispromoted accordingly.

Although high frequency power having the frequency 27 MHz has beenapplied to the upper electrode 21 and high frequency power having thefrequency 800 kHz to the lower electrode 5 in the above-describedembodiment, other frequencies may be set, depending upon kinds ofprocess gas.

It is desirable that high frequency power applied to the lower electrode5 has a frequency lower than the inherent lower ion transit frequency orlower than 1 MHz and that high frequency power applied to the upperelectrode 21 has a frequency higher than the inherent upper ion transitfrequency or higher than 10 MHz. When so arranged, ions are moreefficiently accelerated with a smaller high frequency power and thefollow-up of ions in the plasma sheath to bias frequencies becomesstable even when the rate of gases mixed and the degree of vacuum in theprocess chamber are a little changed. Therefore, ions can be madeincident onto the wafer without scattering in the plasma sheath, therebyenabling a finer work to be achieved at high speed.

According to the present invention, the follow-up of ions is moreexcellent due to the high frequency power applied to he first electrodeand they can be more efficiently accelerated with a smaller power. Inaddition, plasma itself can be kept stable. A more stable treatment canbe thus realized even when the degree of vacuum in the process chamberand the rate of gases mixed change.

Further, when the dissociation is controlled not to progress to theextent greater than needed and the phase of the high frequency powerapplied to the first electrode is also controlled, ions or radicalsneeded for the treatment can be created at a desired timing and they canbe made incident onto the wafer. Anisotropic etching treatment having ahigh aspect rate can be thus attained. In addition, damage applied tothe wafers can be reduced. Further, plasma density can be made highwithout raising the high frequency power and its frequency, and ioncontrol can be made easier.

A second embodiment will be described referring to FIG. 6. Samecomponents as those in the above-described first embodiment will bementioned only when needed.

An etching treatment apparatus 100 has, as high frequency power appliermeans, two high frequency power supplies 141, 151 and a transformer 142.The primary side of the transformer 142 is connected to the first powersupply 141 and then earthed. Its secondary side is connected to both ofthe upper and lower electrodes 21 and 105. A first low pass filter 144is arranged between the secondary side and the upper electrode 21 and asecond low pass filter 145 between the secondary side and the lowerelectrode 105. The first power supply 141 serves to apply high frequencypower having the relatively low frequency such as 380 kHz to theelectrodes 105 and 21. When silicon oxide (SiO₂) film is to be etched,it is optimum that a frequency f₀ of high frequency power applied fromthe first power supply 141 is 380 kHz and when polysilicon (poly-Si)film is to be etched, it is preferably in a range of 10 kHz-5 MHz.

The transformer 142 has a controller 143, by which the power of thefirst power supply 141 is distributed to both electrodes 105 and 21 atan optional rate. For example, 400 W of full power 1000 W can be appliedto the suscepter 105 and 600 W to the upper electrode 21. In addition,high frequency powers whose phases are shifted from each other by 180°are applied to the suscepter 105 and the upper electrode 21.

The second power supply 151 serves to apply high frequency power havingthe high frequency such as 13.56, for example, to the upper electrode21. It is connected to the upper electrode 21 via a capacitor 152 andthen earthed. This plasma generating circuit is called P mode one. It isoptimum that a frequency f₁ of high frequency power applied from it is13.56 MHz, preferably in a range of 10-100 MHz.

It will be described how silicon oxide film (SiO₂) on the silicon waferW is etched by the above-described etching apparatus 100.

The wafer W is mounted on the suscepter 105 and sucked and held there bythe electrostatic chuck 11. The process chamber 102 is exhausted whileintroducing CF₄ gas into it. After its internal pressure reaches about10 mTorr, high frequency power of 13.56 MHz is applied from the secondpower supply 151 to the upper electrode 21 to make CF₄ gas into plasmaand dissociate gas molecules between the upper electrode 21 and thesuscepter 105. On the other hand, high frequency power of 380 kHz isapplied from the first power supply 141 to the upper and lowerelectrodes 21 and 105. Ions and radicals such as fluoric ones inplasma-like gas molecules are thus drawn to the suscepter 105, therebyenabling silicon oxide film on the wafer to be etched.

The generating and keeping of plasma itself are attained in this case bythe high frequency power having a higher frequency and applied from thesecond power supply 151. Stable and high density plasma can be thuscreated. In addition, activated species in this plasma are controlled bythe high frequency power of 380 kHz applied to the upper and lowerelectrodes 21 and 105. Therefore, a more highly selective etching can beapplied to the wafer W. Ions cannot follow up to the high frequencypower which has the frequency of 13.56 MHz and by which plasma isgenerated. Even when the output of the power supply 151 is made large togenerate high density plasma, however, the wafers W cannot be damaged.

The first and second low pass filters 144 and 145 are arranged on thesecondary circuit of the transformer 142. This prevents the highfrequency power having the frequency of 13.56 MHz and applied from thesecond power supply 151 from entering into the secondary circuit of thetransformer 142. Therefore, the high frequency power having thefrequency of 13.56 MHz does not interfere with the one having thefrequency of 380 kHz, thereby making plasma stable. Blocking capacitorsmay be used instead of the low pass filters 144 and 145. Although highfrequency powers have been continuously applied to the electrodes in theabove case, modulation power which becomes strong and weak periodicallymay be applied to the electrodes 21 and 105.

A third apparatus 200 will be described with reference to FIG. 7. Samecomponents as those in the above-described first and second embodimentswill be mentioned only when needed.

A high frequency power circuit of this apparatus 200 is different fromthat of the second embodiment in the following points: A suscepter 205of the apparatus 200 is not earthed; no low pass filter is arranged onthe secondary circuit of a transformer 275; and a second transformer 282is arranged on the circuit of a second power supply 281.

The second power supply 281 serves to generate high frequency power of 3MHz, It is connected to the primary side of the transformer 282, whosesecondary side are connected to upper and lower electrodes 21 and 205. Acontroller 293 which controls the distribution of power is also attachedto the secondary side of the transformer 282.

It will be described how the etching treatment is carried out by theapparatus 200.

High frequency powers of 3 MHz whose phases are shifted from each otherby 180° are applied from the power supply 281 to the suscepter 205 andthe upper electrode 21 to generate plasma between them. At the sametime, high frequency powers of 380 kHz whose phases are shifted fromeach other by 180° are applied from a power supply 274 to them. Ions inplasma generated are thus accelerated to enter into the wafer W.

Further, the two high frequency power supplies 274 and 281 in the thirdapparatus are arranged independently of the other. In short, they are ofthe power split type. Therefore, they do not interfere with each other,thereby enabling a more stable etching treatment to be realized.

Furthermore, high frequency powers are supplied from the two powersupplies 274 and 281 to both of upper and lower electrodes 21 and 205,respectively. The flow of current can be thus concentrated on a narrowarea between the upper 21 and the lower electrode 205. As the result, ahigh density plasma can be generated and the efficiency of controllingions in plasma can be raised.

A fourth embodiment will be described, referring to FIGS. 8 through 12.Same components as those in the above-described embodiments will bementioned only when needed.

As shown in FIG. 8, an etching apparatus 300 has a cylindrical orrectangular column-like air-tight chamber 302. A top lid 303 isconnected to the side wall of the process chamber 302 by hinges 304.Temperature adjuster means such as a heater 306 is arranged in asuscepter 305 to adjust the treated face of a treated substrate W to adesired temperature. The heater 306 is made, for example, by inserting aconductive resistance heating unit such as tungsten into an insulatingsintered body made of aluminium nitride. Current is supplied to thisresistant heating unit through a filter 310 to control the temperatureof the wafer W in such a way that the treated face of the wafer W israised to a predetermined temperature.

A high frequency power supply 319 is connected to the suscepter 305through a blocking capacitor 318. When the wafer W is to be etched, thehigh frequency power of 13.56 MHz is applied from the power supply 319to the suscepter 305.

The suscepter 305 is supported by a shaft 321 of a lifter mechanism 320.When the shaft 321 of the lifter mechanism 320 is extended andretreated, the suscepter 305 is moved up and down. A bellows 322 isattached to the lower end of the suscepter 305 not to leak gases in theprocess chamber 302 outside.

Reaction products deposit in the process chamber 302. A ring 325 isfreely detachably attached to the outer circumference of the suscepter305. It is made preferably of PTFE (teflon), PFA, polyimide or PBI(polybenzoimidazole). It may also be made of such a resin that hasinsulation in a temperature range of common temperature -500° C. or ofsuch a metal like aluminium that has insulating film on its surface. Abaffle plate 326 is made integral to it. A plurality of holes 328 areformed in the baffle plate 326. They are intended to adjust the flow ofgames in the process chamber 302, to make its exhaust uniform, and tomake a pressure difference between the treatment space and a spacedownstream the flow of gases. A top portion 327 of the ring 325 is bentinwards, extending adjacent to the electro-static chuck 11, to make thetop of the suscepter 305 exposed as small as possible.

An upper electrode 330 is arranged above the suscepter 305. When theetching treatment is to be carried out, the suscepter 305 is lifted toadjust the interval between the suscepter 305 and the upper electrode330. The upper electrode 330 is made hollow and a gas supply pipe 332 isconnected to this hollow portion 331 to introduce CF₄ gas and othersfrom a process gas supply supply 333 into the hollow portion 331 througha mass flow controller (MFC) 334. A diffusion plate 335 is arranged inthe hollow portion 331 to promote the uniform diffusion or scattering ofprocess gases. Further, a process gas introducing section 337 having aplurality of apertures 336 is arranged under the diffusion plate 335. Anexhaust opening 340 which is communicated with an exhaust systemprovided with a vacuum pump and others is formed in the side wall of theprocess chamber 302 at the lower portion thereof to exhaust the processchamber 302 to an internal pressure of 0.5 Torr, for example.

When the wafer W is etched in the process chamber 302, reaction productsare caused and they adhere to the ring 325 and the baffle plate 326,leaving the outer circumference of the suscepter 305 substantially freefrom them. When the etching treatment is finished, the wafer W iscarried out of the process chamber 302 into the load lock chamber 43. Anext new wafer W is then carried from the load lock chamber 43 into theprocess chamber 302 and etched in it. When this etching treatment isrepeated many times, a lot of reaction products adhere to the ring 325.

As shown in FIG. 9, the top lid 303 of the process chamber 302 is openedand the ring 325 is detached from the suscepter 305. Reaction productsare then removed from the ring 325 by cleaning.

The time at which the ring 325 must be cleaned is determined as follows:

the number of particles adhering to the wafer W which has been treatedby the apparatus 300 is counted and when it becomes larger than apredetermined value;

the number of particles scattering in the atmosphere exhausted from theapparatus 300 and/or at least in one or more areas in the exhaust pipeis counted and when it becomes larger than a predetermined value;

when predetermined sheets of the wafer W have been treated in theapparatus 300; and

when the total of hours during which plasma has been generated or theplasma treatment has been carried out reaches a predetermined value.

Dry or wet cleaning is used. The dry cleaning is carried out in such away that ClF₃, CF₄ or NF₃ gas is blown to the ring 325 which is leftattached to the suscepter 305 or which is detached from the suscepter305 and left outside the process chamber 302, as shown in FIG. 10.

On the other hand, the wet cleaning is carried out in such a way thatthe ring 325 to which reaction products have adhered is immersed incleaning liquid 351 in a container 350, as shown in FIG. 11. IPA(isopropyl alcohol), water or fluorophosphoric acid is used as cleaningliquid 351. The ring 325 from which reaction products have been removedby the dry or wet cleaning is again attached to the suscepter 305 andthe plasma treatment is then repeated.

When the wafers W are to be etched, plural rings 325 are previouslyprepared relative to one suscepter 305. If so, cleaned one can beattached to the suscepter 305 while cleaning the other.

The dry or wet cleaning can be appropriately used to remove reactionproducts from the ring 325. When the dry cleaning is compared with thewet one, however, the former is easier in carrying out it but itscleaning is more incomplete. To the contrary, the latter is moreexcellent in cleaning the ring 325 but its work is relatively moretroublesome. Therefore,it is desirable that the wet cleaning isperiodically inserted while regularly carrying out the dry cleaning.

The baffle plate will be described referring to FIGS. 12 and 13.

As shown in FIG. 12, it is preferable that an effective diameter D₁ isset not larger than a diameter D₂. The effective diameter D₁ representsa diameter of that area where the process gas jetting apertures 336 arepresent, and the diameter D₂ denotes that of the wafer W in this case.When the effective diameter D₁ is set in this manner, a high efficientetching can be attained in the process chamber 302. It is the mostpreferable that the effective diameter D₁ is set to occupy about 90% ofthe diameter D₂.

Providing that the underside 338 of the upper electrode has a diameterD₃, the effective diameter D₁, the diameter D₂ and the diameter D₃ meetthe following inequality (1).

    D.sub.1 <D.sub.2 <D.sub.3                                  (1)

When the ring the whole of which is made of insulating material is usedas it is, the effective area of the lower electrode becomessubstantially smaller than that of the upper electrode, thereby makingplasma uneven. This problem can be solved when the effective area of thelower electrode is made same as that of the upper electrode or when itis made larger than that of the upper electrode.

As shown in FIG. 13, the baffle plate 326 is made integral to the ring325. It is divided into a portion 360 equal to the diameter D₄ andanother portion 361 larger than it, and the inner portion 360 is made ofmetal such as alminium and stainless steel while the outer portion 361of PTFE (teflon), PEA, polyimide, PBI (polybenzoimidazole), otherinsulating resin or alumite-processed aluminium.

The diameter D₄ is made same as or larger than the diameter D₃. At leastthe inner portion 360 of the baffle plate 326 is positioned just underthe upper electrode 330. The ring 326 is divided into an upper half 363and a lower half 364, sandwiching an insulator 362 between them. Theupper half 363 is made of metal such as aluminium and stainless steeland it is made integral to the inner portion 360 of the baffle plate326. A power supply 319 which serves to apply high frequency power tothe suscepter 305 is connected to these inner portion 360 of the baffleplate 326 and upper half 363 of the ring 325 by a lead 367 via ablocking capacitor 318. At least those portions (the inner portion 360of the baffle plate and the upper half 363 of the ring) which arepositioned just under the upper electrode 330 are made same inpotential. In order to make it easy to exchange the ring 325, it ispreferable that the lead 367 is connected to the upper half 363 of thering or the inner portion 360 of the baffle plate 326 by aneasily-detached socket 368. A lower suscepter 365 is insulated from theupper one 305 by an insulating layer 366. The lower half 364 of the ringis also therefore insulated from the upper half 363 thereof by theinsulator 362.

When at least that portion of the baffle plate 326 which is positionedjust under the upper electrode 330 is made same in potential as thesuscepter 305, as described above, plasma can be made uniform.

Referring to FIGS. 14 and 15, it will be described how the side opening41 of the process chamber 302 through which the wafer W is carried inand out is opened and closed as the suscepter is moved up and down.

The ring 325 provided with the baffle plate 326 encloses the suscepter305. The lifter means 320 is arranged under the process chamber 302 andthe suscepter 305 is supported by the shaft 321 of the lifter means 320.

When the suscepter 305 is moved down, as shown in FIG. 14, the baffleplate 326 is positioned lower than the side opening 41. When it is movedup, as shown in FIG. 15, the baffle plate 326 is positioned higher thanthe side opening 41.

When the suscepter 305 is moved down and the baffle plate 326 ispositioned lower than the side opening 41, therefore, the wafer W can befreely carried in and out of the process chamber 302 through the sideopening 41. When the baffle plate 326 is positioned higher than the sideopening 41 at the time of etching treatment, however, the side opening41 is shielded from the process space between the upper and the lowerelectrode, thereby preventing plasma from entering into the side opening41.

As shown in FIG. 16, it may be arranged that a shielding plate 370 isattached to the outer circumference of the baffle plate 326 and that theside opening 41 is closed by the shielding plate 370 when the suscepter305 is moved up. Particularly, the side opening 41 is too narrow forhands to be inserted. Therefore, inert gas may be supplied, as purgegas, into a clearance 371 between the shielding plate 370 and the innerface of the process chamber 302 not to is cause process gases to enterinto the side opening 41. Similarly, purge gas may also be supplied intoa clearance 372 between the wafer-mounted stage 305 and the upper half363 of the ring 325.

The side opening 41 may be closed by a shielding plate 373 attached tothe outer circumference of the baffle plate 326, as shown in FIG. 17,when the baffle plate 326 is lifted half the side opening 41.

Referring to FIGS. 18 through 28, the cleaning of a fifth CVD apparatuswill be described. Same components as those in the above-describedembodiments will be mentioned only when needed.

A CVD apparatus 500 has a process chamber 502 which can be exhaustedvacuum. A top lid 503 is connected to the side wall of the processchamber 502 by hinges 505. A shower head 506 is formed in the centerportion of the top lid 503 at the underside thereof. A process gassupply pipe 507 is connected to the top of the shower head 506 tointroduce mixed gases (SiH₄ +H₂) from a process gas supply 508 into theshower head 506 through a mass flow controller (MFC) 510. A plurality ofgas jetting apertures 511 are formed in the bottom of the shower head506 and process gases are supplied to the wafer W through theseapertures 511.

An exhaust pipe 516 which is communicated with a vacuum pump 515 isconnected to the side wall of the process chamber at the lower portionthereof. A laser counter 517 which serves to count the number ofparticles contained in the gas exhausted from the process chamber 502 isattached to the exhaust pipe 516. The process chamber 502 isdecompressed to about 10⁻⁶ Torr by the exhaust means 515.

The process chamber 502 has a bottom plate 521 supported by asubstantially cylindrical support 520 and cooling water chambers 522 areformed in the bottom plate 521 to circulate cooling water suppliedthrough a cooling water pipe 523 through them.

A suscepter 525 is mounted on the bottom plate 521 through a heater 526and these heater 526 and the wafer-mounted stage 525 are enclosed by aheat insulating wall 527. The heat insulating wall 527 has amirror-finished surface to reflect heat radiated from around. The heater526 is heated to a predetermined temperature or 400-2000° C. by voltageapplied from an AC power supply (not shown). The wafer W on the stage525 is heated to 800° C. or more by the heater 526.

An electrostatic chuck 530 is arranged on the top of the wafer-mountedstage 525. It comprises polyimide resin films 531, 532 and a conductivefilm 533. A variable DC voltage supply (not shown) is connected to theconductive film 533.

A detector section 538 of a temperature sensor 537 is embedded in thesuscepter 525 to successively detect temperature in the wafer-mountedstage 525. The power of the AC power supply which is supplied to theheater 526 is controlled responsive to signal applied from thetemperature sensor 537. A lifter 541 is connected to the suscepter 525through a member 543 to move it up and down. Those portions of a supportplate 546 through which support poles 544 and 545 are passed areprovided with bellows 547 and 548 to keep the process chamber 502air-tight.

A cover 560 is freely detachably attached to the shower head 506. It ismade of material of the PTFE (teflon) group, PFA, polyimide, PBI(polybenzoimidazole) or polybenzoazole, which are insulators and heatresistant. In the case of the plasma CVD apparatus, the wafer-mountedstage 525 is heated to about 350-400° C. at the time of plasma processand in the case of the heat CVD apparatus, it is usually heated higherthan 650° C. or to about 800° C. The cover 560 is therefore made of sucha material that can resist this radiation heat.

As shown in FIG. 19, a large-diameter opening 563 is formed in a bottom561 of the cover 560. When the cover 560 is attached to the shower head506, the gas jetting apertures 511 of the shower head 506 appear in theopening 563.

As shown in FIG. 20, a plurality of apertures 565 may also be formed inthe cover 560. These apertures 565 are aligned with those of the showerhead 506 in this case.

As shown in FIG. 21, recesses 570 may be formed in the outercircumference of the shower head 506 while claws 571 are formed on aninner circumference 562 of the cover 506, as shown in FIG. 22. The claws571 are fitted into recesses 570 in this case while elasticallydeforming the cover 560. The three claws 571 are arranged on the innercircumference 562 of the cover 560 at a same interval, as shown in FIG.22.

As shown in FIG. 23, the cover 560 may be attached to the shower head506 in such a way that bolts 575 are screwed into recesses 573 of theshower head 506 through a cover side 562.

It will be described how upper electrode cover is cleaned.

When mixed gases (SiH₄ +H₂), for example, are introduced into theprocess chamber 502 to form film on the wafer W, reaction productsadhere to the upper electrode cover 560. As shown in FIG. 24, the toplid 503 is opened and the cover 560 is detached from the shower head506. The cover 560 is then immersed in cleaning liquid 581 in acontainer 580 (wet cleaning). Or the dry cleaning may be conducted insuch a way that cleaning gas such as ClF₃, CF₄ or NF₃ gas is introducedinto the process chamber 502 while keeping the cover 560 attached to theshower head 506.

The time at which the cleaning must be conducted is determined asfollows. The number of particles contained in the gas exhausted throughthe exhaust pipe 516 is counted by the counter 517 and when it becomeslarger than a limit value, the cleaning of the cover 560 must bestarted.

As shown in FIG. 26, the underside of the top lid 503 may be covered bya cover 585, in addition to the shower head 506. Or the inner face ofthe process chamber 502 may be covered by a cover 586, in addition tothe shower head 506, as shown in FIG. 27. An opening 587 is formed inthe cover 586 in this case, corresponding to the side opening 41 of theprocess chamber 502. Or a cover 590 having a curved bottom 591 may beused, as shown in FIG. 28.

A sixth embodiment will be described referring to FIGS. 29 through 34.Same components as those in the above-described embodiments will bementioned only when needed.

As shown in FIG. 29, a magnetron type plasma etching apparatus 600 has arotary magnet 627 above a process chamber 602. Upper and lowerelectrodes 624 and 603 are opposed in the process chamber 602. Processgases are introduced from a gas supply supply 629 to the space betweenthe upper and the lower electrode through an MPC 630. The rotary magnet627 serves to stir plasma generated between both of the electrodes 603and 624.

A suscepter assembly comprises an insulating plate 604, a cooling block605, a heater block 606, an electrostatic chuck 608 and a focus ring612. A conductive film 608c of the electrostatic chuck 608 is connectedto a filter 610 and a variable DC high voltage supply 611 by a lead 609.The filter 610 is intended to cut high frequencies. An internal passage613 is formed in the cooling block 605 and liquid nitrogen is circulatedbetween it and a coolant supply supply (not shown) through pipes 614 and615. A gas passage 616 is opened at tops of the suscepter 603, theheater 617 and the cooling block 605, passing through the suscepterassembly. The base end of the gas passage 616 is communicated with aheat exchanger gas supply supply (not shown) to supply heat exchangergas such as helium gas to the underside of the wafer W through it. Theheater block 606 is arranged between the suscepter 603 and the coolingblock 605. It is shaped like a band-like ring and it is several mmthick. It is a resistant heating unit. It is connected to a filter 619and a power supply 620.

Inner and outer pipes 621a and 521b are connected to the suscepter 603and the process chamber 602. They are conductive double pipes, the outerone 621a of which is earthed and the inner one 621b of which isconnected to a high frequency power supply 623 via a blocking capacitor622. The high frequency power supply 623 has an oscillator foroscillating the high frequency of 13.56 MHz. Inert gas is introducedfrom a gas supply supply (not shown) into a clearance between the inner621a and the outer pipe 621b and also into the inner pipe 621b.

Except the upper electrode, the inner faces of the top of the processchamber 602 is covered by an insulating protection layer 625, 3 mm ormore thick. Similarly, the inner face of its side wall is covered by aninsulating protection layer 626, 3 mm or more thick.

In the conventional magnetron type plasma etching apparatus, the flow ofelectrons tends to gather near the inner wall of the process chamber, asshown in FIG. 34. The flow of plasma is thus irradiated in a directionW, that is, to the side wall of the process chamber, thereby damagingit. In the above-described apparatus 600, however, the side wall of theprocess chamber 602 is covered by the insulating protection layer 626 sothat it can be protected.

Process gas supply and exhaust lines or systems of the apparatus 600will be described.

A process gas supply pipe 628 is connected to the side wall of theprocess chamber 602 at the upper portion thereof and CF₄ gas isintroduced from a process gas supply 629 into the process chamber 602through it. An exhaust pipe 633 is also connected to the side wall ofthe process chamber 602 at the lower portion thereof to exhaust theprocess chamber 602 by an exhaust means 631, which is provided with avacuum pump. A valve 632 is attached to the exhaust pipe 633.

As shown in FIG. 30, a baffle plate 635 is arranged between the outercircumference of the suscepter 603 and the inner wall of the processchamber 602. Plural holes 634 are formed in the baffle plate 635 toadjust the flow of exhausted air or gas.

As shown in FIG. 31, each hole 634 is tilted. Therefore, the conductanceof gas rises when it passes through the holes 634 and the gradient ofelectric field becomes gentle accordingly. This prevents discharge frombeing caused in the holes 634 and plasma from flowing inward under thebaffle plate 635.

As shown in FIG. 32, holes 634a, 634b, 634c and 634d each having a samepitch may be formed in plural baffle plates 635a, 635b, 635c and 635d toform a step-like exhaust hole 634A. This exhaust hole 634A can be formedwhen the baffle plates 635a, 635b, 635c and 635d are placed one upon theothers in such a way that the holes 634a, 634b, 634c and 634d are alittle shifted from their adjacent ones. When these exhaust holes 634Aare formed, abnormal discharges in plasma generation can be moreeffectively prevented.

In the conventional apparatus, each hole 692 in the baffle plate extendsonly vertical, as shown in FIG. 33. These holes 692 allow plasma to flowinward under the baffle plate and abnormal discharges such as sparklesto be caused in them, thereby causing metal contamination and particles.In the apparatus 600, however, the holes 634 are directed toward theexhaust opening 633. The reduction of exhaust speed can be thusprevented. When the direction in which the turbo-pump 631 is driven ismade reverse to the flow of exhausted gas, that is, when it is madeanticlockwise in a case where exhausted gas flows clockwise, the speedof exhausted gas can be raise to a further extent.

A seventh embodiment will be described referring to FIGS. 35 through 43.TEOS gas is used to form film on the wafer W in this seventh plasma CVDapparatus. Same components as those in the above-described embodimentswill be mentioned only when needed.

The plasma CVD apparatus 700 has a cylindrical or rectangular processchamber 710, in which a suscepter 712 is arranged to hold a wafer W onit. It is made of conductive material such as aluminium and it isinsulated from the wall of the process chamber 710 by an insulatingmember 714. A heater 716 which is connected to a power supply 718 isembedded in it. The wafer W on it is heated to about 300° C. (or filmforming temperature) by the heater 716. The process chamber is of thecold wall type in this case, but it may be of the hot wall type. Theprocess chamber of the hot wall type can prevent gas from beingcondensed and stuck.

The electrostatic chuck 11 is arranged on the suscepter 712. Itsconductive film 12 is sandwiched between two sheets of film made ofpolybensoimidazole resin. A variable DC high voltage power supply 722 isconnected to the conductive film 12. A focus ring 724 is arranged on thesuscepter 712 along the outer rim thereof.

A high frequency power supply 728 is connected to the suscepter 712 viaa matching capacitor 726 to apply high frequency power having afrequency of 13.56 MHz or 40.68 MHz to the suscepter 712.

An upper electrode 730 serves as a plasma generator electrode and alsoas a process gas introducing passage. It is a hollow aluminium-madeelectrode and a plurality of apertures 730a are formed in its bottom. Ithas a heater (not shown) connected to a power supply 731. It can be thusheated to about 150° C. by the heater.

A process gas supply line or system provided with a vaporizer (VAPO) 732will be described referring to FIGS. 35 and 36.

Liquid TEOS is stored in a container 734. At the film forming process, aliquid mass flow controller (LMFC) 736 is controlled by a controller 758to control is the flow rate of liquid TEOS supplied from the container734 to the vaporizer 732.

As shown in FIG. 36, a porous and conductive heating unit 744 is housedin a housing 742 of the vaporizer 732. The housing 742 has an inlet 738and an outlet 740. The inlet 738 is communicated with the liquid supplyside of the container 734. The outlet 740 is communicated with thehollow portion of the upper electrode 730.

The heating unit 744 is made of sintered ceramics in which conductivematerial such as carbon is contained, and it is porous. It is preferablyexcellent in workability and in heat and chemical resistance. Terminals747 are attached to it and current is supplied from a power supply 746to it through them. When current is supplied to it, it isresistance-heated to about 150° C. Further, vibrators 748 are embeddedin the housing 742, sandwiching the heating unit 744 between them. It ispreferable that they are supersonic ones. The power supply 746 for theheating unit 744 and a power supply (not shown) for the vibrators 748are controlled by the controller 758.

It will be described how the vaporizer 732 is operated.

When liquid TEOS is supplied from the container 734 to the vaporizer732, it enters into holes in the porous heating unit 744 and it isheated and vaporized. Because its contact area with the porous heatingunit 744 becomes extremely large, its vaporized efficiency becomesremarkably higher, as compared with the conventional vaporizers.

Further, vibration is transmitted from vibrators 748 to liquid TEOScaught by the heating unit 744 and in its holes. Heat transfer face andliquid vibrations are thus caused. Therefore, the border layer betweenthe heat transfer face of each hole in the heating unit 744 and liquidTEOS, that is, the heat resistance layer is made thinner. As the result,convection heat transmission is promoted to further raise the vaporizedefficiency of liquid TEOS.

According to the vaporizer in this case, gas-like TEOS is moved bypressure difference caused between the inlet 738 and the outlet 740 andthus introduced into the process chamber 710 without using any carriergas.

A bypass 750 and a stop valve 752 may be attached to the passageextending from the outlet 740 of the vaporizer, as shown in FIG. 35. Thebypass 750 is communicated with a clean-up unit (not shown) via a bypassvalve 754. The clean-up unit has a burner and others to removeunnecessary gas components. Further, a sensor 756 is also attached tothe passage extending from the outlet 740 to detect whether or notliquid TEOS is completely vaporized and whether or not gases are mixedat a correct rate. Detection signal is sent from the sensor 756 to thecontroller 758.

The operation of the above-described CVD apparatus 700 will bedescribed.

The wafer W is carried into the process chamber 710 which has beendecompressed to about 1×10⁻⁴ -several Torr, and it is mounted on thesuscepter 712. It is then heated to 300° C., for example, by the heater716. While preparing the process chamber 710 in this manner, liquid TEOSis vaporized by the vaporizer 732. High frequency power is applied fromthe high frequency power supply 728 to the lower electrode 712 togenerate reactive plasma in the process chamber. Activated species inplasma reach the treated face of the wafer W to thereby form P-TEOS(plasma-tetraethylorthosilicate) film, for example, on it.

Other vaporizers will be described referring to FIGS. 37 through 41.

As shown in FIG. 37, a vaporizer 732A may be made integral to an upperelectrode 730A of a process chamber 710A. It is attached integral to theupper electrode 730A at the upper portion thereof with an intermediatechamber 770 formed under it. Its housing 742A has a gas outlet side 774in which a plurality of apertures 772 are formed.

A gas pipe 776 is communicated with the intermediate chamber 770 in theupper electrode 730A to introduce second gas such as oxygen and inertgases into it. A bypass 750A extends from that portion of the upperelectrode 730A which is opposed to the gas pipe 776 to exhaustunnecessary gas from the upper electrode 730A. Further, plates 780a,780b and 780c in which a plurality of apertures 778a, 778b and 778c areformed are arranged in the lower portion of the intermediate chamber 770with an interval interposed between them.

As shown in FIGS. 38 and 39, a liquid passage 782 is formed in a heatingunit 744B in the case of a vaporizer 732B. It includes a center passage782a and passages 782b radically branching from the center passage 782a.When it is formed in the heating unit 744B in this manner, it enablesliquid to be uniformly distributed in the whole of the porous heatingunit 744B, thereby raising gas vaporized efficiency to a further extent.

After liquid is vaporized by a vaporizer 738C, two or more gases may bemixed, as show In FIG. 40. A second gas supply opening 784 is arrangeddownstream the vaporizer 738C and second gas component such as oxygenand inert gases is supplied through it. A gas mixing duct 786 extendsdownstream it and a bypass 750C having a bypass valve 754C, and a stopvalve 752C are further arranged in the lower portion of the gas mixingduct 786. A strip-like member 788 is housed in the gas mixing duct 786to form a spiral passage 790 in it. First and second gas components arefully mixed, while passing through the spiral passage 790, and theyreach a point at which the bypass 750 branches from the passageextending to the side of the process chamber.

In addition to TEOS (tetraethylorthosilicate), trichlorsilane (SiHCl₃),silicon tetrachloride (SiCl₄), pentaethoxytantalum (PEOTa: Ta(OC₂ H₅)₅),pentamethoxytantalum (PMOTa: Ta(OCH₃)₅), tetrasopropoxytitanium(Ti(i-OC₃ H₇)₄), tetradimethylaminotitanlum (TDMAT: Ti(N(CH₃)₂)₄),tetraxisdiethylaminatitanium (TDEAT: Ti(N(C₂ H₅)₂)₄), titaniumtetrachloride (TiCl₄), Cu(HFA)₂ and Cu(DPM)₂ may be used as liquidmaterial to be vaporized. Further, Ba(DPM)₂ /THF and Sr(DPX)₂ /THF maybe used as thin ferroelectric film forming material. Water (H₂ O),ethanol (C₂ H₅ OH), tetrahydrofuran (THF: C₄ H₈ O) anddimethylaluminiumhydride (DMAH: (CH₃)₂ AlH) may also be used.

A vaporizer 819 may be attached to a batch type horizontal plasma CVDapparatus 800, as shown in FIG. 41. This CVD apparatus 800 includes aprocess chamber 814 provided with an exhaust opening 810 and a processgas supply section 812, a wafer boat 816 and a heater means 818.Connected to the process gas supply section 812 are a process gas supplyline or system having a liquid container 815, a liquid mass flowcontroller 817 and a vaporizer 815. This vaporizer 819 is substantiallysame in arrangement as the above-described one 732.

As shown in FIG. 42, a conventional vaporizer 731 has a housing 702which is kept under atmospheric pressure and which is filled with aplurality of heat transmitting balls 703 each being made of material,excellent in heat transmission. These heat transmitting balls 703 areheated higher than the boiling point of liquid material by an externalheater means (not shown) to vaporise liquid material Introduced frombelow. Carrier gas is introduced into the vaporizer 701 to carryvaporized process gases.

In the conventional vaporizer 701, however, gas flow rate becomesexcessive at the initial stage of gas supply, that is, overshooting iscaused. FIG. 43 is a graph showing how gas flow rates attained by theconventional and our vaporizers change at the initial stage of gassupply, in which time lapse is plotted on the horizontal axis and gasflow rates on the vertical axis. A curve P represents results obtainedby the conventional vaporizer and another curve Q those obtained by ourpresent vaporizer. As apparent from FIG. 43, gas flow rate overshoots apredetermined one V₁, in the case of the conventional vaporizer, afterthe lapse of 10-20 seconds since the supply of gas is started. In theabove-described vaporizer used by the present invention, however, itreaches the predetermined flow rate V₁ without overshooting it.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, representative devices, andillustrated examples shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. A plasma treatment apparatus for plasma-treatinga substrate under a reduced pressure, comprising:a chamber electricallyconnected to ground; gas supply means for supplying a process gas intosaid chamber; exhaust means for exhausting the chamber; a lowerelectrode on which said substrate is disposed; an upper electrodemounted within the chamber to face said lower electrode; a first powersupply connected to the lower electrode through a first matching circuitto apply a high frequency signal to the lower electrode, said highfrequency signal having a first frequency f₁ lower than an inherentlower ion transit frequency of the process gas; a second power supply togenerate a high frequency signal having a second frequency f₂ higherthan an inherent upper ion transit frequency of the process gas; and anamplitude modulation circuit connected to each of said first and secondpower supplies for receiving high frequency signals having the first andsecond frequencies f₁ and f₂, the amplitude of the high frequency signalhaving the second frequency f₂ being modulated by the high frequencysignal having the first frequency f₁, and said amplitude-modulatedsignal being applied to the upper electrode through the second matchingcircuit.
 2. The plasma treatment apparatus according to claim 1, furthercomprising a phase controller for shifting the phase of the highfrequency signal having the first frequency f₁.